This invention is directed toward containers and container preforms, and more particularly to multi-layer containers and multi-layer container preforms.
Multi-layer containers are typically manufactured for allowing the use of different materials in each of the layers, wherein each material has a specific property adapted to perform the specific function of the layer. The multi-layer containers are manufactured in a variety of ways as represented in the following devices and methods.
For example, U.S. Pat. No. 4,741,936 discloses a laminated preform for a multi-layer polyester bottle. In forming the preform, the process includes forming by co-extrusion a pipe having inner and outer layers of polyester composed mainly of ethylene terephthalate units and an intermediate layer of an oxygen-barrier resin interposed between the inner and outer layers. An adhesive resin is also preferably interposed between adjacent layers. The thickness of the layers of the multi-layer pipe are sized to be uniform. The process for forming the preform includes cooling the outer portion of the molten multi-layer pipe by contact with water and simultaneously introducing an inert gas into the interior of the pipe to cool the inner portion. The pipe is later draw-formed into a multi-layer drawn bottle. The multi-layer bottle disclosed in U.S. Pat. No. 4,741,936, while including a plurality of layers having different properties for different functions, discloses no process or device for causing thickness variations at selected portions of the bottle and on selected layers. Accordingly, the thicknesses at each portion of the bottle are limited by the feasibility of the same thickness at other portions, thereby decreasing the usefulness of the container.
U.S. Pat. No. 4,646,925 discloses a multi-layer preform for draw forming a bottle which is formed by injection molding. The preform includes a neck portion having an open end and a part for engagement with a lid member. It further includes a thick barrel portion to be drawn and a closed bottom portion, wherein the neck portion and the inner wall of the bottom and barrel portions are integrally formed of a thermoplastic polyester. A thin intermediate layer composed of a gas-barrier thermoplastic resin is formed on the inner walls of the barrel and bottom portions so that the top end of the intermediate layer is extended to a point just below the neck portion. An outer layer of thermoplastic polyester is formed in such a positional relation so that the outer layer covers the intermediate layer. A joint is formed directly on the intermediate layer between the outer layer and the neck portion just below the neck portion. Being that the preform is formed by injection molding, thickness variation is directly dependent upon the shape of the mold. Therefore, a particular thickness design cannot be formed unless a new mold is also formed thereby decreasing the freedom for thickness variation for facilitating different functions.
Because the different portions of containers perform different functions, it is often desirable to vary the thickness of the container walls at the specific portion depending upon its function. For example, where a portion of a container is used for supporting the entire container, a thicker wall thickness might be preferred for additional strength. However, such additional thickness may not be desirable in other portions of the container, such as the sidewalls, due to such factors as desired flexibility, transparency and efficiency in material use. Therefore, for single-layer and multi-layer containers, it is often desirable to vary the thickness of the various layers at different portions of the container.
U.S. Pat. No. 3,869,056 discloses a multi-layered hollow plastic container. The container disclosed has an inner thermoplastic layer and an outer pressure molded layer. The container also has an integral open neck or rim portion wherein the thickness of the layers at the neck and rim portion are greater than the thickness of the layers in the remainder of the container. At the upper end of the container, the inner layer of the container overlaps the outer layer of the container at the neck or rim portion. While this patent discloses a container having variable thickness at the neck portion in comparison to the remaining portions of the container, such variable thickness is not applicable to other portions.
In addition, the barrier layer is generally an expensive material so that it is desirable to utilize a relatively thin layer for the barrier while at the same time assuring its viability as a barrier.
There exists a need, therefore, in the container manufacturing art, for a preform and container having multiple layers of material wherein the layers serve the functions of the container and a process for accomplishing the same. There also exists a need to provide such a preform and container with desirable properties, as heat resistance, oxidation resistance and CO.sub.2 resistance, at a reasonable cost and in a simple and convenient manner.